The present invention relates to a method for annealing metal components which are in a partially finished condition.
Thus, the present invention relates to a method for thermally treating metal components at a temperature of 200.degree. - 300.degree. C. With certain metal components which are partially finished, in particular partially finished brass components, the possibility of corrosion or other defective structures occurring in the components due to stresses therein can be eliminated by thermally relieving the stresses. However, up to the present time it has not been possible to relieve these stresses with a thermal treatment of the above type while at the same time achieving a continuous operation with a high output and with a desirable low cost.
It is known, for example, to provide thermal treatment of the above type by utilizing a salt bath which at a temperature of between 200.degree. and 300.degree. C has a sufficiently low viscosity. With such a treating bath it is possible to treat the articles quickly, within minutes, with the components being successively introduced into the bath rapidly one after the other so that it is possible to treat in this way, in suitable stages, partially finished products which are in the process of being manufactured into finished products, such metal components being made of aluminum alloy, for example. Such methods, however, are extremely expensive and carry with them the disadvantage that the salt bath will attack many non-ferrous metals. Furthermore, after the thermal treatment of the partially finished components in the above manner, it is necessary to remove from the components, by washing, the salt which otherwise clings to the components, and this removal of the salt results in considerable difficulties particularly in connection with cleaning of the washing water and in connection with the unavoidable lengthening of the total treating time.
Furthermore, it is known to make use of trivalent or tetravalent alchohols, or mixtures thereof, for the above purposes. However, such methods are also expensive and thus have not been widely used.
Also, known baths of molten metal have proved to be unsuitable because of the ease with which metal components, particularly non-ferrous metal components, dissolve in such molten metal baths.
It is also known to use, for the above purposes oil and fats which are heated so as to provide the thermal treatment. However, in practice such materials have also not been used since at the required temperatures of between 200.degree. and 300.degree. C, these treating materials have a high vapor pressure and therefore easily vaporize. Moreover, such treating baths have not been used because they quickly deteriorate and are rendered useless as a result of oxidation.
It is also known to treat partially finished metal components thermally in furnaces in which hot air is circulated. However, such furnaces have their own peculiar drawbacks because of the thermal properties of the hot air, the small heat capacity and poor heat transfer, and because of the relatively long heating time required for the components which are treated. Thus, with such methods it is essential, in order to achieve a technically useful output, to treat stacks of semifinished products simultaneously.
However, when treating such stacks of products, the heat treatment is not uniform because a much longer treatment is required for those components which are situated at the interior of the stack, as compared with those components which are at the exterior of the stack. The result is that particularly long dwelling periods of the stacked components, on the order of 5-6 hours, are required, with little possibility of achieving the desired treatment at a low cost and with a lack of uniform treatment of all the components. Furthermore, it is not possible to situate structures, which operate in this way on stacks of components, in an automatically operating series of units which act on the components to finish them in accordance with mass production techniques. In other words, it is not possible to situate such structures along a production line.